The present invention relates to a method and apparatus for writing on and reading an optical recording medium.
Recently, optical disks, cards and tapes are developed and have been used for recording information optically. Especially, optical disks are given attention as a medium having large capacity and high density.
A conventional method for writing an optical disk is explained below referring to the figures. FIG. 27 shows an example of an optical disk using a phase-change type recording film. A substrate 2301, which is made of a glass or plastic material such as PMMA or polycarbonate, is provided with guide grooves 2302 and pits indicating an address or other information. This area with the pit train is called the ID area. The guide grooves are formed in concentric circles or a coil from the inner to outer portions of the substrate. Areas 2307 between the grooves are called lands. The ID areas are located at a predetermined pitch along the guide grooves. The areas between the ID areas are called sectors. A surface of the substrate 2301 is provided with layers of a protective film 2303, a recording film 2304 and a reflection film 2305 formed by sputtering or other methods. Furthermore, a protective sheet is glued onto the layers.
A method for writing on and reading the above-mentioned optical recording medium is explained below referring to the figures. FIG. 28 shows a block diagram of a conventional writing and reading apparatus. FIG. 29 shows the write and read operation for an optical disk. In FIG. 29, (a) indicates a write data signal, (b) indicates a laser-driving signal (corresponding to a laser power), (c) indicates a recorded state of the optical disk, and (d) indicates a record format.
The reading process for the optical disk is performed as follows. A system controller circuit 101 drives a spindle motor 114 that rotates the optical disk 113. An optical head 112 focuses a laser beam with a weak power (Pr in FIG. 29) to irradiate the optical disk 113, tracking the guide groove 2302 and the pit train 2502 shown in (c) of FIG. 29. The intensity of the beam reflected by the optical disk 113 varies in accordance with the existence of the pit train 2502 and record marks 2501. Detecting the intensity of the reflected beam generates read signal 122, which is processed into binary data by a read signal processor circuit 115 and demodulated by a demodulator circuit 116. Then the signal is processed in an error correction and deinterleaving circuit 117 to obtain read data. The deinterleaving process restores the original data from the interleaved data, which are changed in order.
The writing process for the optical disk is performed as follows. A system controller circuit 101 connected to a host computer gives write data 102 to an error correction and interleaving circuit 103, which adds error correcting data, i.e., parity bits to the write data, and performs an interleaving process. The interleaving process makes error correction easy by converting a burst error (long continuous error) due to a defect of the optical disk into a random error (short error). The write data are divided into blocks and the order of the blocks is changed according to a predetermined rule in the interleaving process. Then a modulator circuit 104 modulates the data in accordance with the (1, 7) RLL modulation method, for example. Consequently, a modulated data signal 105 is obtained for writing the data area 604 shown in (d) of FIG. 29.
In the synthesizer circuit 109, each data block to be written into each sector is provided with VFO ;and RESYNC signals from a synchronizing signal generator circuit 108 as well as dummy data from a dummy data generator circuit 107 if necessary, to make the write data signal 118. The VFO and RESYNC are synchronizing signals for generating a clock signal synchronizing with the read signal in a PLL circuit (synchronizing signal generator) in the read signal processor circuit 115. The VFO signal is added to the head of the modulated data, and the RESYNCH signal is added in the modulated data signal at a predetermined interval. The dummy data are added for reducing a deterioration of the recording film generated at the end of writing when writing on the same sector repeatedly. The dummy data is not required to include any information. The example of the write data signal 118 is shown in (a) of FIG. 29.
Corresponding to the write data signal 118, the laser driver circuit 110 generates a laser driving signal 111 to drive a laser in the optical head 112, modulating the intensity of the laser beam. An example of the laser-driving signal 111 is shown in (b) of FIG. 29.
When the optical head 112 irradiates the recording film of the optical disk 113 with the focused laser beam having a high intensity (Pp shown in (b) of FIG. 29) for a predetermined period, the temperature of the recording film rises above the melting point and drops rapidly. As a result, the melted spot becomes a recorded mark 2501 (shown in (c) of FIG. 29) having an amorphous state due to rapid cooling. On the contrary, when the recording film is irradiated with the focused laser beam having a middle intensity (Pb shown in (b) of FIG. 29) for a predetermined period, the temperature of the recording film rises to the temperature below the melting point but above the crystallization point. Then the irradiated spot is cooled gradually and assumes a crystalline state.
A recorded pattern having crystalline and amorphous spots as mentioned above, which corresponds to the modulated data signal 105, is created in the data area 604 on the guide groove 2302. Thus, writing and reading of information are performed using a difference of reflectivity between the crystalline and amorphous states.
As shown in (d) of FIG. 29, there is a gap area 602 between the ID area 601 and the VFO area 603, as well as a buffer area 606 between the dummy data area 605 and the next ID area 601. The gap area 602 generates a time for controlling the laser power, and the buffer area 606 compensates for a difference of recording position due to rotation variability of the spindle motor.
When scanning an ID area 601 between sectors 607 of the optical disk, address data are read by the laser irradiating the optical disk with the same weak power as the reading power.
The system controller circuit has a configuration shown in FIG. 30. Transmission of write data and read data between a host computer and the write/read apparatus is performed using a write data buffer 2601 and read data buffer 2602 respectively. The read data is given to the read data buffer 2602 as well as an address data detector circuit 2603. An address data detecting signal is transmitted to the write data buffer 2601 and the read data buffer 2602. A motor driver circuit 2604 drives the spindle motor.
When writing on the optical disk repeatedly as mentioned above, a quality of the read signal of the written data in a sector may be deteriorated at a certain part. Especially, writing similar data into the same sector repeatedly makes the deterioration serious because that part of the sector undergoes repeated melting and hardening while another part never melts. As a result, the thickness of the recording film changes at the boundary of the two parts, so that the thermal and optical characteristics are deteriorated at the boundary. In this case, it is difficult to record (write) and reproduce (read) data properly.
There is a writing method to solve the above-mentioned problem proposed in the Japanese laid-open patent application (Tokukaihei) 2-94113. This method writes data while varying the start point for writing a sector at random within a predetermined range. This range is called the variation range in this specification.
In this writing method, however, the variation range of the start point for writing was constant for various recording media or conditions. On the other hand, the deterioration rate of the recording film depends not only on the number of repeating writings but also on the recording medium or recording condition.
Therefore, the above-mentioned writing method in the prior art is not enough for improving the deterioration of the recording film in every case. For example, when overwriting the optical disk, the whole sector is overwritten. Therefore, even if the data to be written are only a small part of the sector, the whole sector is overwritten actually. A directory area of the disk is overwritten repeatedly with similar data. Thus, the directory area has a tendency to have its recording film deteriorated earlier than another area (called the general area in this specification).
Increasing the variation range of the start point for writing may reduce the deterioration of the recording film. However, an area for writing VFO or dummy data is decreased in a sector because the data area should be settled in the sector. In other words, when adding the VFO area for generating synchronizing data to the head of the data area, and adding the dummy data area to the tail of the data area, the length of the VFO area or the dummy data area have to be shortened in accordance with the enlarged variation range of the start point for writing. Therefore, the deterioration of the recording film at the start and end points of the sector may become critical when being written repeatedly, so that reading of the written data becomes difficult at a certain deterioration level of the recording film. As a result, the number of overwriting of the optical disk may be lowered.